Sealed compressor

ABSTRACT

A sealed compressor of the present invention comprises an electric component ( 105 ); a compression component ( 107 ); and a sealed container ( 101 ) accommodating the electric component ( 105 ) and the compression component ( 107 ); wherein the compression component ( 107 ) includes: a cylinder block ( 115 ) defining a compression chamber ( 135 ); a piston ( 125 ); and a valve plate ( 133 ) having a suction hole ( 137 ) through which a refrigerant gas to be compressed in the interior of the compression chamber ( 135 ) flows, and a discharge hole ( 139 ) through which the refrigerant gas compressed in the interior of the compression chamber  8135 ) is discharged; wherein the piston ( 125 ) is provided with a projection ( 155 ) on a tip end surface ( 153 ) which faces the valve plate ( 133 ); and wherein the projection ( 155 ) is configured such that side surfaces thereof include at least one flat surface and a gradient α of the flat surface with respect to the tip end surface of the piston ( 125 ) is smaller than a gradient β of another side surface of the projection ( 155 ) with respect to the tip end surface of the piston ( 125 ).

TECHNICAL FIELD

The present invention relates to a sealed compressor for use in arefrigeration cycle such as an electric refrigerator, an airconditioner, and a refrigerator-freezer.

BACKGROUND ART

In recent years, energy-saving refrigerators for household use have beendeveloped. Sealed compressors incorporated into the refrigerators forhousehold use have been developed to attain higher efficiency.

Under the circumstances, conventionally, there is a sealed compressorincorporated into the refrigerator for household use, in which toimprove efficiency, a piston is provided with a projection to reduce adead volume of a discharge hole, to reduce a loss which would otherwisebe caused by re-expansion of a compressed gas, and to thereby suppress areduction of a refrigeration ability (see, e.g., Patent Literature 1).

FIG. 7 is a longitudinal sectional view of the conventional sealedcompressor disclosed in Patent Literature 1. FIG. 8 is a perspectiveview of a piston of the conventional sealed compressor. FIG. 9 is across-sectional view of major components of the conventional sealedcompressor, which is taken along A-A of FIG. 8.

As shown in FIGS. 7 to 9, a conventional sealed compressor 1 includes acompression component 5 and an electric component 7 which areaccommodated into a sealed container 3, and its internal space is filledwith a refrigerant gas 9.

The compression component 5 has a configuration in which a piston 13 isreciprocatingly inserted into a cylinder 11 of a substantiallycylindrical shape, and is connected to an eccentric shaft 19 of acrankshaft 17 via a connecting means 15.

A valve plate 25 having a suction hole 21 and a discharge hole 23 isprovided at an end portion of the cylinder 11. The valve plate 25 isprovided with a suction valve (not shown) and a discharge valve 27 toopen and close the suction hole 21 and the discharge hole 23,respectively.

The cylinder 11, the valve plate 25 and the piston 13 define acompression chamber 29. According to a rotation of the crankshaft 17 fortransmitting a rotational power of the electric component 7, the piston13 reciprocates inside of the cylinder 11, which constitute acompression mechanism for suctioning the refrigerant gas 9 into thecompression chamber 29, compressing the refrigerant gas 9 in thecompression chamber 29, and discharging the refrigerant gas 9 out of thecompression chamber 29.

As shown in detail in FIGS. 8 and 9, the conventional sealed compressor1 is configured such that the piston 13 is provided with a projection 31on an end surface (tip end surface) at the valve plate 25 side in aposition in which the projection 31 enters (moves into) the dischargehole 23, to reduce a dead volume (region expressed as meshed pattern) ofthe discharge hole 23.

To reduce a change in the refrigerant gas 9 in a flow direction 39 ofthe refrigerant gas 9, side surfaces of the projection 31 of the piston13 are set such that a gradient thereof changes continuously in acircumferential direction, is minimum in a region of a side surface 33and is maximum in a region of a side surface 35.

An inner peripheral surface 37 of the discharge hole 23 has a gradient(slope) set so that the inner peripheral surface 37 is substantiallyparallel to the side surface 33 and the side surface 35 of theprojection 31 of the piston 13.

Regarding a fluid technique, there is known a book which discloses atechnique for reducing a loss of the fluid in a peripheral region of anentrance of a discharge hole through which the fluid is discharged,which loss is caused by a flow of the fluid, by forming a bell mouthhaving a circular-arc cross-section in the peripheral region of theentrance (see, e.g., Non-patent Literature 1).

CITATION LIST Patent Literature

-   U.S. Pat. No. 5,980,223 specification

Non-Patent Literature

-   Non-patent Literature 1: Basic Engineering Fluid Dynamics Third    revision version (Baifukan 1990 p. 184 to 185)

SUMMARY OF INVENTION Technical Problem

In the structure shown in FIG. 9, the side surface 33 having a gentleslope (small gradient) in the projection 31 can reduce a change in therefrigerant gas 9 in the flow direction 39. However, since theprojection 31 has a truncated cone shape, a portion of the refrigerantgas 9 which should flow from the suction hole 21 to the discharge hole23 flows toward peripheral walls (side surfaces) of the projection 31.

Because of this, on an end surface (tip end surface) of the projection31, portions of the refrigerant gas 9 flowing from the entire sidesurfaces interfere with each other, which causes a turbulent(disordered) flow. This results in a situation in which some of therefrigerant gas 9 does not flow out of the compression chamber 29 intothe discharge hole 23, but is left in the interior of the compressionchamber 29, and the refrigerant gas 9 left (remaining) in the interiorof the compression chamber 29 without being discharged re-expandsaccording to a suction operation of the piston 13. As a result, asuction loss or the like is generated. Under the circumstances, the deadvolume cannot be reduced effectively, and the flow of the refrigerantgas cannot be improved effectively in the sealed compressor 1.

It is assumed that the configuration disclosed in the above mentionedNon-patent Literature 1 is applied to the discharge hole 23 of the abovedescribed conventional sealed compressor 1. However, it is estimatedthat adequate advantages cannot be expected due to a loss of therefrigerant gas (complicated behavior of the refrigerant gas) in thevicinity of the discharge hole 23, which is associated with theprojection 31.

The present invention is directed to solving the above described problemassociated with the prior art, and an object of the present invention isto provide a sealed compressor which can attain a high efficiency, inwhich a dead volume is reduced to reduce a loss caused by re-expansionof a refrigerant gas, and a flow of the refrigerant gas is improved toreduce a loss of a discharged refrigerant gas in an interior of acompression chamber and a discharge hole.

Solution to Problem

To solve the problem associated with the prior art, a sealed compressorof the present invention comprises an electric component; a compressioncomponent actuated by the electric component; and a sealed containeraccommodating the electric component and the compression component;wherein the compression component includes: a cylinder block defining acompression chamber; a piston which reciprocates in an interior of thecompression chamber; and a valve plate disposed to close an opening endof the compression chamber and having a suction hole through which arefrigerant gas to be compressed in the interior of the compressionchamber flows into the interior of the compression chamber, and adischarge hole through which the refrigerant gas compressed in theinterior of the compression chamber is discharged from the interior ofthe compression chamber; wherein the piston is provided with aprojection on a tip end surface which faces the valve plate; and whereinthe projection is configured such that side surfaces thereof include atleast one flat surface and a gradient α of the flat surface with respectto the tip end surface of the piston is smaller than a gradient β ofanother side surface of the projection with respect to the tip endsurface of the piston.

In this configuration, since the projection provided on the tip endsurface of the piston enters (moves into) the discharge hole, a deadvolume can be reduced, and re-expansion of the refrigerant gas can bereduced. As a result, efficiency of the compressor can be improved. Inaddition, in the flow of the refrigerant gas from the suction holetoward the discharge hole, the refrigerant gas collides against the flatsurface and is prevented from flowing toward the peripheral wallsextending in an axial direction of the projection. The refrigerant gascan be efficiently guided toward the discharge hole along the flatsurface. Therefore, the amount of the refrigerant gas left in theinterior of the compression chamber without being discharged, at the endof a compression stroke, can be lessened, and a suction loss which wouldotherwise be caused by re-expansion of the refrigerant gas left in theinterior of the compression chamber without being discharged, can bereduced.

Advantageous Effects of Invention

A sealed compressor of the present invention is capable of reducing aloss of a flow of a discharged gas in an interior of a compressionchamber and a discharge hole and of reducing a suction loss which wouldotherwise be caused by re-expansion of the refrigerant gas left in theinterior of the compression chamber without being discharged. Therefore,the sealed compressor of the present invention can increase itsefficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a sealed compressor accordingto Embodiment 1.

FIG. 2 is a perspective view showing major components of a piston of thesealed compressor according to Embodiment 1.

FIG. 3 is a cross-sectional view of the piston of the sealed compressoraccording to Embodiment 1, which is taken along B-B of FIG. 2.

FIG. 4 is a schematic view showing a tip end surface of the piston ofthe sealed compressor according to Embodiment 1, when viewed from adirection in which the piston retracts.

FIG. 5 is a view showing a characteristic indicating a relationshipbetween a gradient α of a side surface of a projection, and coefficientof performance COP in the sealed compressor according to Embodiment 1.

FIG. 6 is a perspective view showing major components of a pistonaccording to a modified example of Embodiment 1.

FIG. 7 is a longitudinal sectional view of a sealed compressor disclosedin Patent Literature 1.

FIG. 8 is a perspective view of a piston of the sealed compressordisclosed in Patent Literature 1.

FIG. 9 is a cross-sectional view of the piston of the sealed compressordisclosed in Patent Literature 1, which is taken along A-A of FIG. 8.

DESCRIPTION OF EMBODIMENTS

A sealed compressor of the present invention comprises an electriccomponent; a compression component actuated by the electric component;and a sealed container accommodating the electric component and thecompression component; wherein the compression component includes: acylinder block defining a compression chamber; a piston whichreciprocates in an interior of the compression chamber; and a valveplate disposed to close an opening end of the compression chamber andhaving a suction hole through which a refrigerant gas to be compressedin the interior of the compression chamber flows into the interior ofthe compression chamber, and a discharge hole through which therefrigerant gas compressed in the interior of the compression chamber isdischarged from the interior of the compression chamber; wherein thepiston is provided with a projection on a tip end surface which facesthe valve plate; and wherein the projection is configured such that sidesurfaces thereof include at least one flat surface and a gradient α ofthe flat surface with respect to the tip end surface of the piston issmaller than a gradient β of another side surface of the projection withrespect to the tip end surface of the piston.

With this configuration, a dead volume formed in the discharge hole canbe reduced, and a suction loss which would otherwise be caused byre-expansion of the refrigerant gas can be reduced. As a result,efficiency of the compressor can be improved. In addition, therefrigerant gas is prevented from flowing toward the side surfaces ofthe projection by the flat surface having the gradient α. Moreover,since the gradient α of the flat surface is set smaller than thegradient β of another side surface, a passage resistance of the flow ofthe refrigerant gas along the flat surface can be reduced.

As a result, the refrigerant gas colliding against the flat surface andis prevented from flowing toward the peripheral walls by the flatsurface can be efficiently guided toward the discharge hole. Therefore,the amount of the refrigerant gas left (remaining) in the interior ofthe compression chamber without being discharged, at the end of acompression stroke, can be lessened, and a suction loss which wouldotherwise be caused by re-expansion of the refrigerant gas left in theinterior of the compression chamber without being discharged, can bereduced. Thus, efficiency of the sealed compressor can be improved.

In the sealed compressor of the present invention, the flat surfacehaving the gradient α may be placed to face the suction hole.

In such a configuration, the refrigerant gas flowing into thecompression chamber through the suction hole can be more efficientlyguided to flow toward the discharge hole along the flat surface. Inparticular, the amount of the refrigerant gas left (remaining) in theinterior of the compression chamber without being discharged, at the endof the compression stroke, can be further reduced. As a result, asuction loss which would otherwise be caused by re-expansion of therefrigerant gas left in the interior of the compression chamber withoutbeing discharged, can be reduced. Thus, efficiency of the sealedcompressor can be further improved.

In the sealed compressor of the present invention, the discharge holemay have an opening area which increases from the compression chamberside toward an opposite side of the compression chamber.

In this configuration, an area of a flow passage defined by the sidesurface of the projection and the inner peripheral surface of thedischarge hole can be increased. Because of this, it becomes possible toreduce a passage resistance of the refrigerant gas flowing through thedischarge hole. As a result, the compressed refrigerant gas can besmoothly discharged from the discharge hole, excessive compression ofthe refrigerant gas during the compression stroke can be reduced, andthe amount of electric power input to the sealed compressor can bereduced.

In the sealed compressor of the present invention, an opening portion ofthe discharge hole in the valve plate, which opening portion is at thecompression chamber side, may have a circular-arc cross-section.

In this configuration, the refrigerant gas can be guided to thedischarge hole more smoothly. As a result, the amount of the refrigerantgas left (remaining) in the interior of the compression chamber withoutbeing discharged, at the end of the compression stroke, can be reduced.Therefore, a suction loss which would otherwise be caused byre-expansion of the refrigerant gas left in the interior of thecompression chamber without being discharged can be reduced, and henceefficiency of the sealed compressor can be further improved.

In the sealed compressor of the present invention, a cross-section ofthe projection which is taken along a plane which is substantiallyparallel to the tip end surface of the piston may have a polygonalshape.

In this configuration, the refrigerant gas collides against plural flatsurfaces defining the polygonal shape, and is prevented from flowingtoward the side surfaces of the projection by the flat surfaces. Theportions of the refrigerant gas colliding against the plural flatsurfaces flow along the flat surfaces, and therefore can be guidedtoward the discharge hole. Thus, the amount of the refrigerant gas left(remaining) in the interior of the compression chamber without beingdischarged, at the end of the compression stroke, can be furtherreduced. As a result, a suction loss which would otherwise be caused byre-expansion of the refrigerant gas left in the interior of thecompression chamber without being discharged can be reduced, and henceefficiency of the sealed compressor can be further improved.

In the sealed compressor of the present invention, a cross-section ofthe projection which is taken along a plane which is substantiallyparallel to the tip end surface of the piston may have a rectangularshape.

In this configuration, the refrigerant gas flowing toward the dischargehole is guided along the four flat surfaces defining the projection.Therefore, the flow to the side surfaces of the projection can besuppressed, and the refrigerant gas can be smoothly guided toward thedischarge hole. Moreover, the amount of the refrigerant gas left(remaining) in the interior of the compression chamber without beingdischarged, at the end of the compression stroke, can be reduced, and asuction loss which would otherwise be caused by re-expansion of therefrigerant gas left in the interior of the compression chamber withoutbeing discharged, can be reduced. As a result, efficiency of the sealedcompressor can be further improved.

In the sealed compressor of the present invention, the gradient α may bein a range of 65 degrees≦α≦80 degrees.

In this configuration, the refrigerant gas can be flowed smoothly towardthe discharge hole. Especially, the amount of the refrigerant gas left(remaining) in the interior of the compression chamber without beingdischarged, at the end of the compression stroke, can be reduced, asuction loss which would otherwise be caused by re-expansion of therefrigerant gas left in the interior of the compression chamber withoutbeing discharged can be reduced, and efficiency of the sealed compressorcan be further improved.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. Throughout the drawings, the same orcorresponding components are designated by the same reference symbols,and will not be described in repetition. In addition, throughout thedrawings, components required to describe the present invention aredepicted and the other components are not illustrated. Moreover, thepresent invention is not limited to the embodiments described below.

Embodiment 1 Configuration of Sealed Compressor

FIG. 1 is a longitudinal sectional view of a sealed compressor accordingto Embodiment 1. FIG. 2 is a perspective view showing major componentsof a piston of the sealed compressor according to Embodiment 1. FIG. 3is a cross-sectional view of the piston of the sealed compressoraccording to Embodiment 1, which is taken along B-B of FIG. 2. FIG. 4 isa schematic view showing a tip end surface of the piston of the sealedcompressor according to Embodiment 1, when viewed from a direction inwhich the piston retracts.

As shown in FIG. 1, in a sealed compressor (hereinafter will be referredto as a compressor) 100, a refrigerant gas 103 is filled into a sealedcontainer 101. The sealed container 101 accommodates a compressioncomponent 107 and an electric component 105 for actuating thecompression component 107. The compression component 107 and theelectric component 105 are elastically supported on the sealed container101 by means of a suspension spring 109.

The compression component 107 mainly includes a crankshaft 111 forconverting a rotational motion of the electric component 105 into areciprocation motion, and a cylinder block 115 including a cylinder 113defining a compression chamber 135 of a substantially cylindrical shape.

The crankshaft 111 includes a main shaft section 119 to which a rotor117 of the electric component 105 is fastened and an eccentric section121 having a center axis which is eccentric with respect to the mainshaft section 119. The main shaft section 119 is supported on a mainshaft bearing unit 123 of the cylinder block 115.

A piston 125 is reciprocatingly inserted into the cylinder 113. Thepiston 125 is connected to the eccentric section 121 of the crankshaft111 via a connecting means 127. That is, one end of the connecting means127 is rotatably connected to the eccentric section 121 of thecrankshaft 111, while the other end thereof is rotatably connected to apiston pin 129 attached to the piston 125. This allows the connectingmeans 127 to convert a rotational motion of the eccentric section 121caused by a rotation of the crankshaft 111 into a reciprocation motionand transmit the reciprocation motion to the piston 125.

A valve plate 133 is attached to an end portion 131 of the cylinder 113.The valve plate 133 closes the end portion 131 (compression chamber 135)of the cylinder 113. The valve plate 133 is provided with a suction hole137 and a discharge hole 139 each of which has a circular opening. Ashape of the discharge hole 139 will be described later.

The valve plate 133 is provided with a suction valve (not shown) foropening and closing the suction hole 137 and a discharge valve 145 (seeFIG. 3) for opening and closing the discharge hole 139. A configuration(shape) of the suction valve and a configuration (shape) of thedischarge valve 145 are well-known, and therefore detailed descriptionthereof will be omitted.

The valve plate 133 is covered with a cylinder head 141. Inside of thecylinder head 141, a discharge chamber 147 communicated with thedischarge hole 139 is provided. A discharge pipe 149 is connected to thedischarge chamber 147. An exit pipe 151 is connected to the dischargepipe 149 such that the exit pipe 151 extends to outside of the sealedcontainer 101. Furthermore, as shown in FIG. 1, a suction muffler 143 isretained between the cylinder head 141 and the valve plate 133.

As shown in FIG. 3, the discharge hole 139 provided in the valve plate133 is formed such that its opening area increases in a direction fromthe compression chamber 135 side toward an opposite side (dischargechamber 147 side) of the compression chamber 135. An opening portion 173of the discharge hole 139 in the valve plate 133, which opening portionis at the compression chamber 135 side, has a circular-arccross-section. In more detail, the cross-section of the opening portion173 which is taken along a direction in which the piston 125 moves has acircular-arc shape which is round. A radius of the circular-arc of theopening portion 173 of the discharge hole 139 may be set as desired.Hereinafter, the opening portion 173 of the circular-arc shape will bereferred to as a bell mouth portion 173.

The discharge hole 139 has a size to allow a projection 155 of thepiston 125 to easily move thereinto. As shown in FIG. 4, the dischargehole 139 is provided in a position of a center axis 159 which iseccentric outward relative to a center axis 157 of the compressionchamber 135.

Therefore, a center axis 161 of the projection 155 is provided in aposition so that the projection 155 closes and exposes the dischargehole 139 during the reciprocation motion of the piston 125, and(substantially) conforms to the center axis 159 of the discharge hole139. That is, the center axis 161 of the projection 155 is in theposition which is eccentric outward relative to the center axis 157 ofthe compression chamber 135 and the center axis 163 of the piston 125(substantially) conforming to the center axis 157.

As shown in FIG. 4, the projection 155 (discharge hole 139) and thesuction hole 137 provided in the valve plate 133 do not overlap witheach other when viewed from the direction in which the piston 125 moves.Specifically, the suction hole 137 is positioned within a projectionplane (hatched region) from a line X which is an extended line of a sideof the projection 155 (bottom of a side wall 165 a as will be describedlater) which is closest to the center axis 163 of the piston 125 to aregion which is beyond the center axis 163 of the piston 125.

As shown in FIGS. 2 to 4, a tip end surface 153 of the piston 125 at thevalve plate 133 side (surface facing the valve plate 133) is providedwith the projection 155 such that the projection 155 overlaps with thedischarge hole 139 when viewed from the direction in which the piston125 moves. The projection 155 is integral with the piston 125, andcloses and exposes the discharge hole 139 according to the reciprocationmotion of the piston 125.

The projection 155 has a rectangular shape in cross-section which istaken along a plane parallel to the tip end surface 153 of the piston125, i.e., substantially rectangular-parallelepiped shape (includingtruncated pyramid shape), and has four flat surfaces (hereinafter willbe referred to as side walls) 165 a, 165 b, 165 c, 165 d, and a topsurface 167. The projection 155 has a shape in which the top surface 167perpendicular to the center axis 163 of the piston 125 has asubstantially rectangular shape.

The projection 155 is configured such that a gradient (slope) formedbetween the four side walls 165 a, 165 b, 165 c, 165 d, and the tip endsurface 153 of the piston 125 is less than 90 degrees. In other words,the projection 155 is configured such that the cross-section which istaken along a plane parallel to the tip end surface 153 of the piston125 has an area which is reduced toward a top portion (top surface 167)which is distant from the tip end surface 153 of the piston 125.

As shown in FIG. 4, the side wall 165 a of the projection 155 isoriented such that an angle θ (hereinafter will be referred to asplacement angle) formed between the line X and a line Y passing throughthe center axis (center) 169 of the suction hole 137 and the center axis(center) 163 of the piston 125, is set to about 52 degrees.

The placement angle θ may be defined as a placement relationship inwhich a line Z which is perpendicular to the side wall 165 a and passesthrough a center of the side wall 165 a crosses the line Y passingthrough the center axis 169 of the suction hole 137 and the center axis163 of the piston 125 at a predetermined angle.

As shown in FIG. 3, a gradient (slope) a formed between the side wall165 a and the tip end surface 153 of the piston 125 is set to 70degrees. According to a result of an experiment as described later, thegradient α may be set to a desired value in a range of 65 degrees≦α≦80degrees, and may be α≦79 degrees. Note that there is a little tolerancein the gradient α because the piston 125 and the projection 155 aremolded using a die.

A gradient (slope) β formed between other side walls 165 b, 165 c, 165d, and the tip end surface 153 of the piston 125 is set to about 85degrees. The gradient β is an angle except for a draft angle (about 5degrees) during the above stated die molding, and may be set to adesired value. The gradient α and the gradient β are set such that thegradient α is smaller than the gradient β.

A curved surface 171 having a specified diameter is formed in a portion(base end portion of the projection 155) of the tip end surface 153 ofthe piston 125 which the side wall 165 a of the projection 155 crosses.In other words, the side wall 165 a of the projection 155 partially hasthe curved surface 171.

[Operation and Advantage of Sealed Compressor]

Next, operation and advantages of the sealed compressor 100 configuredas described above will be described. In the compressor 100, as shouldbe well-known, a refrigerant circuit connecting a condenser (not shown),a pressure-reducer (not shown), and an evaporator (not shown) isconnected between a suction pipe (not shown) and the exit pipe 161, thusconstituting a well-known refrigeration cycle. As the refrigerant gas103 to be compressed, R600 a is used.

When the electric component 105 is supplied with an electric current,the rotor 117 rotates and the crankshaft 111 rotates. A rotationalmotion of the eccentric section 121 of the crankshaft 111 is transmittedto the piston 125 via the connecting means 127. This causes the piston125 to reciprocate inside of the cylinder 113.

In a suction (intake) stroke in which the piston 125 moves from a topdead center toward a bottom dead center, the volume of the compressionchamber 135 increases according to the motion of the piston 125 towardthe crankshaft 111. Therefore, the pressure in the interior of thecompression chamber 135 decreases. Due to a pressure difference betweenan interior of the suction muffler 143 and the interior of thecompression chamber 135, the suction valve (not shown) opens, so thatthe compression chamber 135 and the suction muffler 143 are communicatedwith each other via the suction hole 137. Thereby, the refrigerant gas109 is guided from the refrigerant circuit to the interior of the sealedcontainer 101, and suctioned into the interior of the compressionchamber 135 through the suction muffler 143 and the suction hole 137.

Then, in a compression stroke in which the piston 125 moves from thebottom dead center toward the top dead center, the volume of thecompression chamber 135 decreases according to the motion of the piston125 toward the valve plate 133. Therefore, the pressure in the interiorof the compression chamber 135 increases. Due to a pressure differencebetween the interior of the suction muffler 143 and the interior of thecompression chamber 135, the suction valve (not shown) closes. Then, therefrigerant gas 103 in the interior of the compression chamber 135 iscompressed, and the pressure in the interior of the compression chamber135 further increases.

When the pressure in the interior of the compression chamber 135increases to a value which is equal to or higher than the pressure inthe interior of the discharge chamber 147, the discharge valve 145 opensdue to a pressure difference between an interior of the dischargechamber 147 and the interior of the compression chamber 135. Until thepiston 125 reaches the top dead center, the compressed refrigerant gas103 is discharged from the discharge hole 139 to the discharge chamber147 inside of the cylinder head 141.

The refrigerant gas 103 discharged to the discharge chamber 147 flowsthrough the discharge pipe 149 and is sent out from the exit pipe 151 tothe refrigerant circuit outside of the sealed container 101, thusforming a refrigeration cycle.

The above described suction, compression and discharge strokes arerepeated each time the crankshaft 111 rotates, and the refrigerant gas103 circulates within the refrigeration cycle.

The flow of the refrigerant gas 103 discharged from the discharge hole139 in the above described discharge stroke, will be described in detailwith reference to FIG. 3. Herein, a description will be given of a casewhere it is assumed that the discharge stroke is included in thecompression stroke based on the motion of the piston 125, for the sakeof convenience.

The piston 125 moves in the direction in which the projection 155 movesinto the discharge hole 139. In a latter half of the compression stroke,as shown in FIG. 3, the tip end surface 153 of the piston 125 getscloser to the valve plate 133, and the projection 155 gets closer to thedischarge hole 139 which faces the projection 155. Then, according to anincrease in the pressure in the interior of the compression chamber 135,the discharge valve 145 opens.

Upon the discharge valve 145 opening, the refrigerant gas 103 compressedin the interior of the compression chamber 135 is discharged to theinterior of the discharge chamber 147 inside of the cylinder head 141all at once via the discharge hole 139, as indicated by arrows in FIG.3.

When the compression stroke progresses, the projection 155 of the piston125 moves into the discharge hole 139. The compression stroke finishesin a state in which a portion of the compressed refrigerant gas 103 isleft within the dead volume (portion expressed as meshed pattern)defined by the projection 155 and the discharge hole 139.

The flow of the refrigerant gas 103 in the interior of the compressionchamber 135 in the compression stroke is a three-dimensional flow inwhich a flow velocity and a flow direction change significantly, andwhich exhibits a complicated behavior. As described above, in thecompressor disclosed in Patent Literature 1, since the projection 31 hasthe truncated cone shape, the refrigerant gas 9 flows toward theperipheral walls (side walls) of the projection 31, which causes aturbulent (disordered) flow.

However, in Embodiment 1, since the projection 155 provided on the tipend surface 153 of the piston 125 has a substantially rectangularparallelepiped shape having the four side walls 165 a, 165 b, 165 c, 165d, the refrigerant gas 103 is less likely to flow toward the peripheralportions of the projection 155.

In particular, at a time point which is near the end of the compressionstroke, a flow passage (portion expressed as meshed pattern in FIG. 3)defined by the discharge hole 139 and the projection 155 is narrower, asthe piston 125 moves in the direction in which the projection 155 movesinto the discharge hole 139. This makes the flow velocity of therefrigerant gas 103 flowing through the flow passage higher. It isestimated that this causes the refrigerant gas in the interior of thecompression chamber 135 to be guided to the discharge hole 139 along theside walls 165 a, 165 b, 165 c, 165 d.

Specifically, the refrigerant gas 103 present in the vicinity of theinner wall of the cylinder 113 flows toward the discharge hole 139 alongthe tip end surface 153 and its flow is blocked by the side walls 165 b,165 d of the projection 155 (collides against the side walls 165 b, 165d of the projection 155). After colliding against the side walls 165 b,165 d, the refrigerant gas 103 flows along the side walls 165 b, 165 dand is guided to inside of the discharge hole 139. It is estimated thatat corner portions formed by the side walls 165 b, 165 d and theadjacent side walls 165 a, 165 c, a turbulent flow occurs, but a flowcomponent guided to inside of the discharge hole 139 increases.

It is also estimated that portions of the refrigerant gas 103 flowingfrom the corner portions toward the side wall 165 c of the projection155 collide against each other, and a portion the refrigerant gas 103 isguided to the discharge hole 139 along the surface of the side wall 165c.

It is estimated that the refrigerant gas 103 flowing toward thedischarge hole 139 along the tip end surface 153 collides against theside wall 165 a, its flow is blocked by the side wall 165 a, and a flowcomponent of refrigerant gas 103 which is guided to the discharge hole139 along the surface of the side wall 165 a increases.

In Embodiment 1, a base portion of the tip end surface 153 of the piston125 from which the projection 155 projects is the curved surface 171.With this structure, it is expected that the flows of the refrigerantgas 103 along the side walls 165 a, 165 b, 165 c, 165 d, can be madesmooth.

It is well known that the volume of the dead volume defined by theprojection 155 and the discharge hole 139 significantly affects theefficiency of the sealed compressor 100. In addition, in the presentinvention, through an experiment, it was discovered that the shape ofthe projection 155 of the piston 125 affects the efficiency of thesealed compressor 100, to a degree equal to or more than that of thevolume of the dead volume.

Hereinafter, advantages achieved by the shape of the projection 155 ofthe piston 125 will be described.

FIG. 5 is a view showing a characteristic indicating a relationshipbetween the gradient α of the side surface of the projection, andcoefficient of performance COP in the sealed compressor according toEmbodiment 1. In FIG. 5, a horizontal axis indicates the gradient αformed between the side wall 165 a of the projection 155 and the tip endsurface 153 of the piston 125, while a vertical axis indicates thecoefficient of performance COP.

A measurement result of FIG. 5 is of the compressor 100 having acylinder volume of 6.0 cc and an operating frequency of 50 Hz. As can beseen from FIG. 5, it was confirmed through the experiment that theefficiency was higher when the gradient α of the side wall 165 a of theprojection 155 was in a range of 65 degrees≦α≦80 degrees.

Next, the experiment result of the gradient α shown in FIG. 5 will beconsidered, and estimation will be made as follows.

Among the four side walls 165 a, 165 b, 165 c, 165 d of the projection155, the gradient α formed between the side wall 165 a facing thesuction hole 137 and having a larger area and the tip end surface 153 ofthe piston 125, is set in a range of 65 degrees≦α≦80 degrees. Thiscauses a passage area of a flow passage defined by the side wall 165 aand the inner peripheral surface of the discharge hole 139 to be greaterthan a passage area of a flow passage defined by each of the side walls165 b, 165 c, 165 d and the inner peripheral surface of the dischargehole 139. Because of this, it becomes possible to reduce a passageresistance in the flow passage defined by the side wall 165 a and theinner peripheral surface of the discharge hole 139, and hence increasethe refrigerant gas 103 guided to the discharge hole 139, along the sidewall 165 a of the projection 155.

Furthermore, the gradient α of the side wall 165 a is set smaller thanthe gradient β of the side walls 165 b, 165 c, 165 d. This reduces apassage resistance of the flow of the refrigerant gas along the sidewall 165 a, which allows the refrigerant gas 103 of a larger amount tobe guided to the discharge hole 139.

That is, the passage resistance of the refrigerant gas 103, which iscaused by the structure in which the projection 155 and the innerperipheral surface of the discharge hole 139 are close to each other, isreduced. In association with this, the flow of the refrigerant gas 103is more effectively faired, the amount of the refrigerant gas 103 leftin the interior of the compression chamber 135 without being discharged,is reduced, and a suction loss which would otherwise be caused byre-expansion of the refrigerant gas 103 left in the interior of thecompression chamber without being discharged, at a time point justbefore the suction stroke starts, is reduced. As a result, electricinput to the compressor 100 can be effectively reduced (coefficient ofperformance COP can be improved).

If the gradient β is set smaller than 65 degrees, the refrigerant gas103 guided toward the discharge hole 139 along the side wall 165 aincreases in amount. However, the refrigerant gas 103 guided toward thedischarge hole 139 along the side wall 165 a interferes with therefrigerant gas 103 guided toward the discharge hole 139 along the sidewall 165 c, causing a turbulent flow. Thereby, all of the refrigerantgas 103 does not flow out of the compression chamber 135 and a portionof the refrigerant gas 103 is left (remains) in the compression chamber135. The refrigerant gas 103 left in the interior of the compressionchamber 135 without being discharged re-expends according to a suctionoperation of the piston 125, and as a result, a suction loss isgenerated. In this way, in the sealed compressor 100, the dead volumecannot be effectively reduced, and the flow of the refrigerant gascannot be effectively improved.

The result of the experiment supports that in addition to the volume ofthe dead volume, the shape of the discharge hole 139, and the shape ofthe projection 155 of the piston 125, the gradient α formed between theside wall 165 a closest to the center axis 169 of the suction hole 137,among the four side walls 165 a, 165 b, 165 c, 165 d of the projection155, and the tip end surface 153 of the piston 125, affects theefficiency of the compressor 100.

It was also confirmed through the experiment that the projection 155 ofEmbodiment 1 is able to improve the efficiency of the compressor 100 inoperating frequencies which is near the operating frequency of 50 Hzdescribed with reference to FIG. 5, although there is a difference inimprovement of efficiency among the operating frequencies.

Therefore, it is expected that the compressor 100 of Embodiment 1 isable to achieve further energy saving in the case of using the settingof the gradient α of the side wall 165 a of the projection 155 andinverter actuation control by plural operating frequencies including 50Hz.

In addition, in Embodiment 1, the refrigerant gas 103 is smoothly guidedtoward the discharge hole 139 by providing the bell mouth portion 173 inthe periphery of the entrance of the discharge hole 139, a loss in theentrance of the discharge hole 139 can be lessened.

The refrigerant gas 103 faired in an axial direction of the dischargehole 139 by the side walls (flat surfaces) 165 a, 165 b, 165 c, 165 d ofthe projection 155 easily flows along the circular-arc contour of thebell mouth portion 173 and smoothly flows through the discharge hole139.

In other words, the flow of the refrigerant gas 103 is made smooth by asynergetic effect produced by the projection 155 and the bell mouthportion 173. Therefore, the refrigerant gas 103 left in the interior ofthe compression chamber 135 without being discharged, at the end of thecompression stroke, is reduced.

Therefore, in addition to the reduction of the dead volume in thedischarge hole 139 because of the projection 155, a loss which wouldotherwise be caused by re-expansion of the refrigerant gas 103 left inthe compression chamber 135 without being discharged, can be reduced,and hence the input to the compressor 100 can be reduced. Although inEmbodiment 1, the valve plate 133 is provided with the bell mouthportion 173, the present invention is not limited to this. The valveplate 133 may not be provided with the opening 173.

Furthermore, in Embodiment 1, by forming the discharge hole 139 suchthat its opening area increases from the compression chamber 135 sidetoward an opposite side of the compression chamber 135 (dischargechamber 147 side), the area of the flow passage defined by theprojection 155 and the inner wall of the discharge hole 139 can beincreased, and thus, the passage resistance of the refrigerant gas 103flowing through the discharge hole 139 can be reduced.

The cross-sectional area of the flow passage defined by the projection155 and the inner wall of the discharge hole 139, which is taken alongthe plane parallel to the tip end surface 153, increases toward an exitof the discharge hole 139 (discharge chamber 147). Because of this, thepassage resistance is reduced, which allows the refrigerant gas 103 toeasily flow into the discharge chamber 147. In this way, the refrigerantgas 103 left in the interior of the compression chamber 135 withoutbeing discharged, at the end of the compression stroke, can be reduced,and hence a loss which would otherwise be caused by re-expansion of therefrigerant gas 103 left in the interior of the compression chamber 135without being discharged, can be reduced. As a result, electric powerinput to the compressor 100 can be reduced in amount.

Although in Embodiment 1 the discharge hole 139 is formed such that itsopening area increases from the compression chamber 135 side toward anopposite side of the compression chamber 135, the present invention isnot limited to this. It is expected that even the discharge hole 139 ofa cylindrical shape having a uniform opening area can improve theefficiency as compared to the conventional sealed compressor 1, althoughthere is some difference in improvement of the efficiency from that ofthe structure in which the opening area increases from the compressionchamber 135 side toward an opposite side of the compression chamber 135.Therefore, this configuration may be used.

Modified Example 1

Next, a sealed compressor of Modified example 1 of Embodiment 1 will bedescribed.

FIG. 6 is a perspective view showing major components of a pistonaccording to modified example of Embodiment 1.

As shown in FIG. 6, the compressor 100 according to Modified example 1has basically the same configuration as that of the compressor 100 ofEmbodiment 1, but is different from the same in shape of the projection155 of the piston 125. Specifically, in Modified example 1, theprojection 155 has substantially a truncated cone shape, and a flatsurface 155 a is formed on a portion of the truncated cone shape. Theflat surface 155 a is formed such that a gradient of the flat surface155 a with respect to the tip end surface 153 of the piston 125 is thegradient α.

The compressor 100 according to Modified example 1 so configured canachieve the same advantages as those of the compressor 100 of Embodiment1.

Numeral modifications and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, the description is to be construedas illustrative only, and is provided for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Thedetails of the structure and/or function may be varied substantiallywithout departing from the spirit of the invention.

INDUSTRIAL APPLICABILITY

A sealed compressor of the present invention is a sealed compressorwhich has a high productivity and a high efficiency and is inexpensive,and is applicable to a sealed compressor for use in a refrigerationcycle and incorporated in various refrigeration units. An articlestorage device incorporating such a sealed compressor is used as variousdevices such as refrigerators for household uses, dehumidificationmachines, show cases, and vending machines, and is applicable as variousstorage devices which can lessen electric power consumption.

REFERENCE SIGNS LIST

-   -   100 sealed compressor    -   101 sealed container    -   103 refrigerant gas    -   105 electric component    -   107 compression component    -   115 cylinder block    -   125 piston    -   133 valve plate    -   135 compression chamber    -   137 suction hole    -   139 discharge hole    -   153 tip end surface    -   155 projection    -   165 a side wall (flat surface)    -   165 b side wall (flat surface)    -   165 c side wall (flat surface)    -   165 d side wall (flat surface)    -   173 bell mouth portion    -   α gradient    -   β gradient

1. A sealed compressor comprising: an electric component; a compressioncomponent actuated by the electric component; and a sealed containeraccommodating the electric component and the compression component;wherein the compression component includes: a cylinder block defining acompression chamber; a piston which reciprocates in an interior of thecompression chamber; and a valve plate disposed to close an opening endof the compression chamber and having a suction hole through which arefrigerant gas to be compressed in the interior of the compressionchamber flows into the interior of the compression chamber, and adischarge hole through which the refrigerant gas compressed in theinterior of the compression chamber is discharged from the interior ofthe compression chamber; wherein the piston is provided with aprojection on a tip end surface which faces the valve plate; and whereinthe projection is configured such that side surfaces thereof include atleast one flat surface and a gradient α of the flat surface with respectto the tip end surface of the piston is smaller than a gradient β ofanother side surface of the projection with respect to the tip endsurface of the piston.
 2. The sealed compressor according to claim 1,wherein the flat surface having the gradient α is placed to face thesuction hole.
 3. The sealed compressor according to claim 1, wherein thedischarge hole has an opening area which increases from the compressionchamber side toward an opposite side of the compression chamber.
 4. Thesealed compressor according to claim 1, wherein an opening portion ofthe discharge hole in the valve plate, which opening portion is at thecompression chamber side, has a circular-arc cross-section.
 5. Thesealed compressor according to claim 1, wherein a cross-section of theprojection which is taken along a plane which is substantially parallelto the tip end surface of the piston has a polygonal shape.
 6. Thesealed compressor according to claim 1, wherein a cross-section of theprojection which is taken along a plane which is substantially parallelto the tip end surface of the piston has a rectangular shape.
 7. Thesealed compressor according to claim 1, wherein the gradient α is in arange of 65 degrees≦α≦80 degrees.